The present study aimed to elucidate the roles of the mitogen-activated protein kinase kinase (MEK)/extra- cellular signal-regulated kinase (ERK) and phosphatidylinositol 3ʼ-kinase (PI3K)/Akt signaling pathways in reg- ulating cisplatin (CDDP)-induced cytotoxicity in ovarian carcinoma cells. We treated seven ovarian carcinoma cell lines (KF, KFr, KOC-2S, SK-OV-3, SHIN-3, TU-OS-3, and TU-OS-4) with CDDP combined with PI3K inhibitor [LY294002 (LY)], MEK inhibitor [PD98059 (PD)], or MEK/ERK activator [phorbol 12-myristate 13-acetate (PMA)], then assessed cell viability, expressions of Akt, phosphorylated (p)Akt, ERK, pERK, and cleaved caspase-3 protein by western blotting, cell cycle distribution, and apoptotic cells by flow cytometric analysis and annexin V staining. Proteins pMEK, pERK, and pAkt were expressed in all cell lines. The range of IC50 to CDDP was 2.4 to 26.9μM for those cell lines. CDDP combined with LY had an additive effect on inhibiting cell growth,whereas combined with PD had an antagonism for all cell lines. Interestingly, growth of cells was dramaticallysuppressed when CDDP was combined with PMA in the CDDP-resistant cells (KFr, SK-OV-3, SHIN-3, TU-OS- 3, TU-OS-4). Treatment with PMA up-regulated protein expression levels of pERK and cleaved caspase-3 only in the CDDP-resistant cells. CDDP combined with PMA increased the S-phase fraction and apoptotic cells inthe CDDP-resistant cells. These results indicate that MEK/ERK activated by PMA may overcome resistance to CDDP in ovarian carcinoma cells.
